In-stream water flows: A perspective from downstream environmental requirements in Tungabhadra river basin

Environmental water requirements, also referred as ‘Environmental Flows’, are compromises between the development of water resources and the maintenance of a river in an ecologically acceptable or agreed condition. Managing environmental water flow is a complex task, because there is change in quantity of water as the flow moves downstream. For instance, between a major storage and the places downstream where water is diverted, the quantity of water in a river may change significantly from the natural condition and the seasonal pattern of flow may also be drastically altered. Further downstream, where a large proportion of the river’s water is removed for human use, it is likely to be reduced by the overall flow levels. This paper assesses the optimum water requirements for better management of a downstream ecosystem based on field investigations and desk study. Three big dams across a river basin have reduced the natural flow in the main river. It has altered the socio economic condition of the downstream dependent population of the Tungabhadra river basin covering two south Indian states –Karnataka and Andhra Pradesh.